1. Field of the Invention
This invention relates to a cyclodextrinase, its preparation process, and a process for preparing maltooligosaccharides using said enzyme.
2. Description of the Prior Art
Few reports are available on the enzyme cyclodextrinase (which is also called cyclomaltodextrinase EC 3.2.1.54). To the present inventors' knowledge, there are merely known the enzyme produced by a microorganism Bacillus macerans (Biochemistry, Vol. 7, pp. 121-124, 1968), and by a microorganism Bacillus coagulans (Agric. Biol. Chem., Vol. 47, pp. 1441-1447, 1983).
Regarding preparation of maltooligosaccharides, a process is known in which the desired oligosaccharides are produced from starch, etc., under the action of amylases capable of producing specified oligosaccharides ranging from glucose to maltohexaose (Arch. Biochem. Biophys., Vol. 155, pp. 290-298, 1973).
There are also known a method for producing such maltooligosaccharides as maltohexaose and higher-order ones (i.e., those with more than 6 glucoside-bonded monosaccharide molecules) by using cyclodextrins as the starting material and cleaving them by acid hydrolysis (Japanese Patent Kokai No. 191690/86), and a method for producing such oligosaccharides as maltoheptaose and higher-order ones, in which the coupling reaction of cyclodextrin and monosaccharide or cyclodextrin and oligosaccharide is catalyzed by using cyclodextrin glucanotransferase (E.C. 2.4.1.19) which is produced by Bacillus macerans (Methods in Enzymology, Vol. 5, pp. 148-155, 1962).
Maltooligosaccharides are not only useful as a substrate for the assay of serum amylase, with their demand for such use increasing, but also their wide application to pharmaceuticals, chemicals and foods, for example as base material of nutritine agent, excipients, bulk fillers, etc., is expected.
However, no amylase is yet known which is capable of specifically producing maltooligosaccharides having a greater number of glucoside-bonded monosaccharide molecules than maltoheptaose from starch, nor is established any efficient method for producing such oligosaccharides according to an enzymatic process using starch as the starting material.
In production of oligosaccharides such as maltohexaose and higher-order ones by using cyclodextrins as the starting material, the method of acid hydrolysis has the problem that a large amount of by-products are generated to excessively reduce the yield of the desired hydrolyzate. Also, the enzymatic method using cyclodextrin glucanotransferase involves the problem that a substantial amount of unreacted cyclodextrin remains in the reaction solution as it is necessary to control the rate of reaction for converting cyclodextrin to the objective product at a low level because of possible decomposition of the product itself or increased build-up of by-products by a coupling reaction between the product and cyclodextrin with the progress of the reaction, and therefore purification of the product becomes difficult.